Deep, persistent problems are never solved by accident; they are solved only by people who are obsessed with them and set out to solve them directly.

Just like an ordinary guitar string, a fundamental string can vibrate in different modes. And it is these different modes of vibration of the string that are understood in string theory as being the different elementary particles.

We know no more than we did in 1975 - and that's not good

Deep, persistent problems are never solved by accident; they are solved only by people who are obsessed with them and set out to solve them directly.

There is nothing outside the universe.

Some string theorists prefer to believe that string theory is too arcane to be understood by human beings, rather than consider the possibility that it might just be wrong.

Having begun my life in science searching for the equation beyond time, I now believe that the deepest secret of the universe is that its essence rests in how it unfolds moment by moment in time.